This invention relates to plastic bags.
Plastic bags are used to contain electronic products. Those electronic products often need very careful handling, such as in clean rooms to avoid contamination. Also, the bags in which the products are to be contained must be appropriately manufactured so as to not introduce contamination. There are also treatments introduced to the bag during its manufacture to benefit the product to be contained. One such treatment is a volatile corrosion inhibitor chemical mixed into the bag raw material before it is formed so that it is contained in the volume of the bag. Consequently the volatile corrosion inhibitor outgasses into the bag interior after the product is put in and the bag is sealed. This protects the product from corrosion during its time in the bag.
Also, such bags may have an antistatic material mixed into the raw material before it is formed and, therefore, contained in the volume of the bag, to discharge static electricity which could damage sensitive electronic components.
All successfully used VCI chemicals have the common property of xe2x80x9cSublimationxe2x80x9d, the ability to go from a solid to a gas without going through a liquid phase. This property is effected by temperature, as an increase in temperature will cause more chemicals to become a gas. By placing the chemical in an enclosure, the entrapped vapor will soon saturate the air causing the reaction to come to equilibrium and slow down or stop any further gas production. Cool and/or cold temperatures slow down both the corrosion reaction and the sublimation reaction.
The most effective enclosures have been made from plastic materials. These materials inherently have good moisture and oxygen barrier properties. The end result is small amounts of VCI produce maximum protection levels. In addition the plastic materials are effective in protecting the metal from dust, dirt and abrasion problems. All together leading to a successful package.
The ability of the VCI materials to work in conjunction with many of the antistatic control additives that are currently used in plastic packaging material, further enhances the successful use of VCI""s in the electronics market. A single material with the dual protective properties offers ideal solutions to most of the industries corrosion and protection problems. Small amounts of VCI materials can be blended with the antistatic additives during production of the plastic part or film.
A further benefit of non-contamination of the surface of an electronic element is experienced with VCI materials. A small amount of the chemical deposit on the metal is quickly removed when the enclosure is removed (the part is taken out of the package). 100% removal is achieved in very little time (15-20 minutes max.). With the miniaturization that has occurred in the electronic industry, contamination has become a huge problem. A super clean package is absolutely required. Testing has proven that VCI chemistry is a safe and effective packaging material for this market.
Plastic film, used in making bags or covers for metal parts, is usually smooth. This can cause a problem in some packages where the geometry of the metal part could expose a smooth side of the metal to contact the smooth plastic. The attraction between two smooth surfaces (van der Waals forces) can cause sticking and/or staining of the metal surfaces. Rough surfaces are not desirable because of abrasion.
In addition, during periods of high humidity a thin layer of moisture will develop inside an enclosure (Green House effect) and a pool of water will develop in these smooth areas effectively blocking the VCI from reaching the metal. Corrosion develops in these areas and is at times a serious problem. A need to protect the metal from this pooling effect is essential to many otherwise good package designs.
Further, there is, in some cases difficulty in inserting the product into the bag due to the surface friction between the bag and the product, or possible snagging of the product on the bag""s interior surface. Also, bags which have flat surfaces may cling to the flat surface of a printed circuit board which can be detrimental to that portion of the printed circuit board.
The present invention provides advantages in the respect of the foregoing problems. During extrusion of the bag, a series of longitudinal ribs are provided integrally with the interior of the bag. These longitudinal ribs provide added volume to the bag and added surface area to the inside of the bag. Consequently, more of the volatile corrosion inhibitor (VCI) can be stored and there is a larger surface area over which to outgas resulting in a greater volume of the VCI gas introduced inside the bag over a shorter time as well as availability of VCI over a longer time. Thus the invention lies in a method of enhancing the storage volume and consequently the rate and time period of outgassing of the VCI by providing longitudinal ribs which increase the total volume of the bag and the interior surface area of the bag.
Similarly, the amount of antistatic material which can be disposed in the bag volume is increased if the bag volume is increased.
Also, the longitudinal ribs allow the product to be inserted into the bag more easily by reducing friction and preventing snagging of corners or other sharp portions of the product on the bag""s interior surface.
Also, the ribs prevent any portion of the bag from clinging to a flat surface, such as a printed circuit board.